RAISING WATER. 



expedients. In this case the bucket is raised by turning the 



winch of the windlass, so that the rope is gradually wound upon 



its axle. The power has Fi g . 2. 



still to raise the weight of 



the rope, to produce its 



flexure on the axle, and to 



overcome the friction of 



the axle of the windlass in 



its bearings. 



In the contrivance of 

 mechanical agents, the first 

 object is always to remove 

 as much as possible all 

 sources by which the moving power is absorbed upon useless 

 objects. In the present case the only useful exertion of the 

 moving force is that which is engaged in raising the water. 

 The useless parts of the force expended, are, first, that 

 absorbed by the weight of the bucket ; secondly, that absorbed 

 by the weight of the rope ; thirdly, that absorbed in bending 

 the rope over the groove of the pulley, or the curvature of the 

 axle ; fourthly, that which is expended on the friction of the 

 axle in its bearings ; fifthly, that which is expended in drawing 

 the bucket aside when it has been elevated, and discharging 

 the water from it into the vessel or reservoir destined to receive 

 it ; and, sixthly, that which is expended in letting down the 

 bucket into the well to be refilled. 



Now when all these sources of waste of power are considered 

 and estimated, and their aggregate amount determined, it will be 

 apparent that they greatly exceed the 

 force expended upon the mere elevation 

 of the water. 



4. A part of the loss of power arising 

 from these causes is sometimes removed 

 by the simple expedient of attaching two 

 buckets to the extremities of the rope 

 which passes over the pulley (fig. 3) 

 established above the well. By these 

 means, while the full bucket is drawn up 

 the empty one descends, and by its weight 

 and that of the rope which descends with 

 it, the weight of the full bucket and the 

 rope which ascends with it is balanced, so 

 that the power has only to act against the . 

 weight of the water, the friction and the 

 resistance to flexure presented by the rope. 



N 2 179 



